The invention relates generally to optics, and more particularly to optic devices used in systems and methods for imaging.
Numerous applications exist that require a focused beam of electromagnetic radiation. For example, energy dispersive X-ray diffraction (EDXRD) may be used to inspect airline baggage for the detection of explosive threats or other contraband. Such EDXRD may suffer a high false positive rate due to weak diffracted X-ray signals. The weakness of the X-ray signals may stem from a variety of origins. First, a portion of the polychromatic X-ray spectrum used in EDXRD is produced by the Bremsstrahlung part of the source spectrum, which is inherently low in intensity. Second, X-ray source collimation may eliminate more than 99.99 percent of the source X-rays incident on the baggage volume under analysis. Third, some of the materials being searched for, e.g., explosives, may not diffract strongly as they are amorphous. Fourth, the diffracting volume may be small. The last two limitations arise from the type of threat materials being searched for in baggage, making all but the second limitation unavoidable. Although discussed in the context of explosives detection, the limitations described above are equally applicable to medical situations.
At lower X-ray energies, such as 60 keV and below, increasing the polychromatic X-ray flux density at the material being inspected has been addressed, for example, by coupling hollow glass polycapillary optics to low powered, sealed tube (stationary anode) X-ray sources. An example of hollow glass polycapillary optics may be found in, for example, U.S. Pat. No. 5,192,869. The glass is the low index of refraction material, and air filling the hollow portions is the high index of refraction material. These types of optics typically do not provide much gain at energy levels above 60 keV, since the difference in the indices of refraction between air and glass, and hence the critical angle for total internal reflection, becomes increasingly small as energy levels approach and surpass 60 keV.
Further, such optics use a concept of total internal reflection to reflect X-rays entering the hollow glass capillaries at appropriate angles back into the hollow capillaries, thereby channeling a solid angle of the source X-rays into collimated or focused beams at the output of the optic. As used herein, the term “collimate” refers to the creation of quasi-parallel beams of electromagnetic (EM) radiation from divergent EM beams. Only about five percent of an EM source's solid angle typically is captured by the input of such known optics.
In addition, the use of air in known optics as one of the materials prevents such optics from being placed within a vacuum. Thus, known optics are limited in their potential uses.
It would thus be desirable for a device that could collect more of the primary electromagnetic radiation from the source and redirect those rays to a desired spot to improve the electromagnetic radiation flux density at that spot.